Conventional energy sources such as coal, oil, natural gas, and uranium, represent a finite resource and furthermore result in adverse consequences in terms of environmental damage and/or risk of damage. Despite some improvements in pollution control and safety protocols, none of these energy sources satisfactorily eliminates environmental concerns. In contrast, renewable energy sources are never exhausted and often more controllable effects or little effect on the environment. Common renewable energy harnessing technologies include photovoltaic systems, solar thermal applications, wind mills, wind energy electricity generators, micro-hydro power plants, biomass/biogas plants, geothermal, wave and tidal plants, and their associated energy storage components. Each of these technologies currently has economic, practical, and/or technical hurdles which prevent their widespread use. Photovoltaic electricity generation has the singular advantage of being modular and not limited to geographic location. For this reason, decentralized electricity generation, and systems of different sizes are possible. The conversion of solar radiation into electrical energy by means of solar cells has been successfully implemented as a part of satellite and space travel technology. Other applications for solar cells such as charging batteries, powering watches, calculators and other devices has also seen modest commercial success.
The theoretical efficiency of solar cells is about 30%, and in practice, efficiencies as high as 25% have been achieved with silicon photovoltaic laboratory devices. Overall system efficiencies of commercial devices are in the range of 10 to 14%. The technology of photovoltaic devices is well developed, but large scale application is hampered by the high price of the cells. The widespread use of solar power has been elusive because it can be difficult and costly to manufacture commercial photovoltaic cells, which are made of inorganic crystals such as silicon.
One alternative to circumvent this problem is to develop photovoltaic cells from materials that can be processed as easily as plastics. Organic solar cells have an advantage over their inorganic counterparts, in that they are much less expensive to produce. They do not require the high deposition temperatures or complex processing as required for inorganic devices, and they can be deposited onto large flexible substrates. For example, organic cells can be made in different colors and be flexible enough to use on window blinds, walls, and other materials in buildings. This provides design options that could lower the cost of using the cells. Unfortunately, poor energy conversion efficiencies have thus far prevented organic-based devices from being successfully commercialized. The last few years have seen a tremendous progress in the application of organic materials for photovoltaic following the success of this class of materials in other electrical, electronic and opto-electrical applications. However, none of the existing techniques provides sufficient improvements in efficiencies and reduced manufacturing costs.